Reusable adhesive that liquefies under UV light Created "Interesting Video"

Adhesives are useful, but once most of them set, that's it — you're committed. Removing them usually means heat, solvents, or just tearing things apart. A team of researchers at Japan's National Institute of Advanced Industrial Science and Technology (AIST) has come up with something fundamentally different: an organic adhesive that can be switched between solid and liquid states simply by shining light on it.

The material works through a photochemical isomerization reaction. When exposed to UV light in the 365–385 nm range, the compound transitions from a solid adhesive state to a liquid. Shine green light on it and it solidifies again — ready to bond once more. The whole process is reversible and can be repeated many times, with no need for heat, cooling, or any chemical treatment. Just light.

How It Works

The underlying mechanism involves molecules that change their shape when they absorb specific wavelengths of light — a process called photoisomerization. In the solid phase, the molecules pack together in an ordered crystalline structure that gives the material its adhesive properties. UV light triggers a molecular flip that disrupts this packing and causes the material to melt into a liquid. Green light reverses the flip, and the material recrystallizes and becomes sticky again.

The fact that this works at room temperature without any thermal input is what makes it practically interesting. Many shape-changing or phase-change materials require significant temperature changes, which limits their usefulness in applications where precise control is needed.

Potential Applications

A reusable, light-switchable adhesive could find uses in electronics assembly, where components sometimes need to be attached and detached precisely without damage. It could also work in medical devices, precision optics mounting, and any situation where adhesion needs to be temporary and controllable. The fact that it uses only light — a clean, contactless stimulus — makes it particularly appealing for delicate or enclosed systems.

Check out the video below to see the material in action:

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Source: Physics World

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Sunscreen patches for wounded skin!!

Latex could one day find its way into
specialised sunscreens © Shutterstock

Scientists in France have made a water-resistant latex film loaded with a UVB filter that could be applied as a thick, uniform layer of sunscreen to wounded skin, which is more susceptible to UV damage.

The film, made of nanostructured latex, was built up of soft-core and hard-shell layers by Aggeliki Triftaridou and colleagues at ESPCI-ParisTech, Paris. An amino acid-based surfactant was used as an emulsifier in the place of volatile organic compounds (VOCs).

Elimination of VOCs, traditionally used for their plasticiser effect, is the concept of this work, as Triftaridou explains: ‘The use of an amino acid-based surfactant as an emulsifier rendered the film environmentally friendly and biocompatible, and conferred better mechanical properties to it.’ In the absence of VOCs, the film was cast by water-evaporation, which meant loading an organic UV absorber was going to be challenging.

The team chose 2-ethylhexyl-4-methoxycinnamate (EMC) as their UV absorber over aesthetically less pleasing inorganic absorbers, such as titanium dioxide, which causes whitening of the skin through UV reflectance.

 EMC is used in more than 75% of sunscreens, is highly water insoluble and rarely results in photoallergic reactions. Triftaridou and her team fed EMC directly into the monomer mixture in the reactor in either the core- or the shell-forming step, successfully loading EMC directly into the films without the need for VOCs.

When exposed to UV light, the EMC-loaded film gave zero transmittance values, which demonstrates its sunscreen properties.

Also, the film was able to completely block UV light after being soaked in water for one month or soaked for one month and exposed to sunlight for four days. The water-resistant property of the film is particularly exciting as Triftaridou points out that ‘unlike common sunscreen formulations, the UVB shielding ability remains intact, even after soaking in water’.

 The film also adapts easily to skin motion and is non-sticky to the touch, which as Triftaridou says originates ‘partially from their lightly cross-linked nature and partially from the presence of a continuous hard phase formed by the shells of the soft-core hard-shell particles’.

Jean-François Lutz, head of the precision macromolecular chemistry group at the Institut Charles Sadron, Strasbourg, France, thinks that ‘there are two main innovations in the work: the water-borne core–shell latex that is easy to make and is environmentally friendly; and the utilisation of these latex films as sunscreens’. He thinks the films provide an ‘excellent alternative to all existing commercial products’, adding that ‘this is a clever material with a real commercial potential’.

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